How to configure Web SSO with Remote Desktop Gateway
in Windows 2012 - Step by step with screenshots

RD Gateway is responsible for the credentials for remote computers. By
default, Remote Desktop Gateway (RD Gateway) is configured to support web
SSO. The deployment RD Gateway property responsible for this is “Use RD
Gateway credentials for remote computers.”

2.
In the Deployment Properties dialog box, select the RD Gateway tab. For web SSO to work
with RD Gateway, select the Use RD Gateway credentials for remote computers
check box, and set the Logon method to Password Authentication.